There is a strong correlation between the membrane fluctuations and the material properties of living cells. The former, consisting of submicron displacements, can be altered by changing the cells' pathophysiological conditions. It is our hypothesis that the material properties of cells can be retrieved when we quantify cell membrane fluctuation and combine that result with an appropriate physical model. We have developed: (1) an optical imaging technique to noninvasively quantify membrane fluctuations in red blood cells at the nanometer and millisecond scales; and (2) a model to retrieve the material properties of red blood cell membrane. The technique employs laser interferometry and provides full-field quantitative topographical information of living cells with unprecedented stability. Integration with the mathematical model provides the specific material properties from individual cell membrane fluctuations: shear modulus of the membrane; bending modulus; and viscosity of the cytoplasm. Employing these methods, we have systemically studied the material properties of human red blood cells altered by various pathophysiological conditions: morphological transition of red blood cell; parasitization by the P. falciparum parasites; and metabolic remodeling of the membrane driven by Adenosine-5'- triphosphate (ATP). We envision that this investigation could offer a means to link cell membrane fluctuations with the pathological conditions that lead to human disease states by quantitatively providing the alternation in material properties. A clear understanding of the mechanical alteration of red blood cells is important to studying the human diseases which cause their infection.